[RFC PATCH 05/10] lib/oe/path: try hardlinking instead of guessing when it might fail

[Vijai Kumar K <Vijaikumar_Kanagarajan@mentor.com>]

From: Henning Schild <henning.schild@siemens.com>

The comparison of the stat st_dev is not enough to judge whether
hardlinking will work. One example would be where you try and hardlink
across two bind-mounts of a directory. The st_dev will be the same and
the operation will still fail.

Instead of implementing a check to try and figure out hardlink support
just try hardlinking and fall back to a copy when running into an
exception.

Signed-off-by: Henning Schild <henning.schild@siemens.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
[Vijai: Imported from OE core f5571bda8327f927feb23b167ab4594b7d0c95bc]
Signed-off-by: Vijai Kumar K <Vijaikumar_Kanagarajan@mentor.com>
---
 meta/lib/oe/path.py | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/meta/lib/oe/path.py b/meta/lib/oe/path.py
index c6bb604..3506e2c 100644
--- a/meta/lib/oe/path.py
+++ b/meta/lib/oe/path.py
@@ -99,7 +99,22 @@ def copyhardlinktree(src, dst):
     if os.path.isdir(src) and not len(os.listdir(src)):
         return
 
-    if (os.stat(src).st_dev ==  os.stat(dst).st_dev):
+    canhard = False
+    testfile = None
+    for root, dirs, files in os.walk(src):
+        if len(files):
+            testfile = os.path.join(root, files[0])
+            break
+
+    if testfile is not None:
+        try:
+            os.link(testfile, os.path.join(dst, 'testfile'))
+            os.unlink(os.path.join(dst, 'testfile'))
+            canhard = True
+        except Exception as e:
+            bb.debug(2, "Hardlink test failed with " + str(e))
+
+    if (canhard):
         # Need to copy directories only with tar first since cp will error if two 
         # writers try and create a directory at the same time
         cmd = "cd %s; find . -type d -print | tar --xattrs --xattrs-include='*' -cf - -S -C %s -p --no-recursion --files-from - | tar --xattrs --xattrs-include='*' -xhf - -C %s" % (src, src, dst)
@@ -121,12 +136,9 @@ def copyhardlinktree(src, dst):
 def copyhardlink(src, dst):
     """Make a hard link when possible, otherwise copy."""
 
-    # We need to stat the destination directory as the destination file probably
-    # doesn't exist yet.
-    dstdir = os.path.dirname(dst)
-    if os.stat(src).st_dev == os.stat(dstdir).st_dev:
+    try:
         os.link(src, dst)
-    else:
+    except OSError:
         shutil.copy(src, dst)
 
 def remove(path, recurse=True):
-- 
2.17.1